ZAMBOANGA, Philippines (AP) — Muslim rebels holding more than 100 people hostage in the southern Philippines exchanged gunfire with government troops Saturday despite efforts by the country’s vice president to arrange a cease-fire and end the six-day standoff.

The standoff began Monday when about 200 fighters from a Moro National Liberation Front rebel faction stormed several coastal communities in Zamboanga city and seized residents. The military says 22 people, including 15 rebels, have since been killed in sporadic clashes between the guerrillas and troops who have surrounded them.

Vice President Jejomar Binay said rebel leader Nur Misuari agreed to a truce late Friday by telephone, and he relayed the news to Defense Secretary Voltaire Gazmin, who has been helping deal with the crisis in Zamboanga city, a major port. Binay said he planned to fly to Zamboanga Saturday to help the negotiations.

But Gazmin said the rebels have continued to fire in violation of the agreement.

“Everybody wants peace, to stop this without more bloodshed,” Gazmin told DZBB radio network. “But as we speak, there’s firing so there’s no cease-fire. We agreed that government forces will not fire only if the MNLF will not open fire.”

President Benigno Aquino III flew to Zamboanga earlier Friday to visit government troops and some of the 24,000 residents displaced by the violence. He warned in a speech that his government won’t hesitate to use force to end the most serious security crisis his administration has faced since he came to power in 2010.

There was also fighting on Friday, and ABS-CBN TV reported that voices presumably of hostages were heard shouting “cease fire, cease fire.” One government soldier was reportedly wounded.

The Moro National Liberation Front rebels have been overshadowed by a rival group in talks with the government for a new minority Muslim autonomy deal.

Misuari signed a peace deal in 1996, but the guerrillas did not lay down their arms and later accused the government of reneging on a promise to develop long-neglected Muslim regions in the predominantly Roman Catholic nation. The government says Misuari kept on stalling and making new demands.

Misuari has not been seen in public since the standoff began.

“There are lines they should not cross,” Aquino said of the rebels. He said the government would be obligated to use “the force of the state” if those lines are crossed.